[Milsurplus] 125 VAC Line? Make Your BA's Happy, Cheap.

[Hubert Miller]

Saw this while cleaning out emails and it is for me timely, as i'd thought recently i should see if there's anything harvestable in this dead UPS here and get it off the floor
and out. My comments -

1. Rereading Mike's wiring instructions, i still don't get it. Of course both primaries are going to the AC input, but in parallel, of course, so what's different here?
2. A bucking transformer configuration is not an autotransformer.
3. But Dave is right about the phenomenon, as any transformer scrounger will verify.
I had an odd one recently. I had a transformer that had powered 4 octal tubes plus a 6X5 rectifier with 2 supposedly 6 volt windings. The removed transformer indicated 11 and 9 volts 
using a DMM. I thought, this ain't right. I found a 6X5 tube and alligator clipped it to the fil windings one at a time and remeasured. The voltages were now 7 volts, about right for a 
1940s transformer. Interestingly, the 220 volt high voltage winding was within 10% of nominal even without being loaded. Using a pointer VOM the discrepancy was not as extreme
but the effect was still there. I think i learned that a good old low-sensitivity low ohms-per-volt meter is just about right for first level checking of power transformers. 
-Hue 

-----Original Message----
From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of Mike Feher
Sent: Thursday, January 14, 2016 10:07 AM
To: 'David Stinson' <arc5 at ix.netcom.com>; milsurplus at mailman.qth.net; boatanchors at mailman.qth.net
Subject: Re: [Milsurplus] 125 VAC Line? Make Your BA's Happy, Cheap.

Dave -

I am not sure I understand what you mean by the need for a load for setting up the magnetic field for an auto transformer. Why hook it up bucking? Just hook it up in series with the input, in an aiding configuration and then put your AC input across both windings and take your output from the low end to the junction of the 15 volt winding. 73 - Mike 

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960 

-----Original Message-----
From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of David Stinson
Sent: Thursday, January 14, 2016 12:01 PM
To: milsurplus at mailman.qth.net; boatanchors at mailman.qth.net
Subject: [Milsurplus] 125 VAC Line? Make Your BA's Happy, Cheap.

Got 125 VAC + on you shack's AC power buss?
Ronnie, W5SUM and I worked this problem.

There must be a zillion old, broken Uninterruptable Power Supply (UPS) units laying around.  These typically have an AC cord going in and AC sockets going out 
plus circuit breaker, etc.   In 99% of the cases, the
transformers in these units are still good and are perfect for building a "line bucker."

We found a couple of dead 12 Amp APC units.
The transformers had a 120 V primary,
a lo-current 15 V and a Hi-current 15 V windings.
The lo-current winding is not used, unless you want to light a pilot light or something.

Pulled the "hot" leads from the dead circuit board and directly powered the transformer through the circuit breaker.  Wired the Hi-current 15 V winding in the "bucking" configuration with one side to the junction of the incoming "hot" and the other side going to the "outgoing Hot" sockets on the back.
Left all neutrals connected together as normal.
If the voltage is boosted instead of bucked, swap the 15V secondary wires.
Mine drops my line voltage from 125 V to 110 V and my boatanchors are happy.
12 A service will run a lot of stuff
and broken UPSs are cheap, so you can add more.

Important Tip:  A transformer "line bucker" acts as an "autotransformer."
To measure the output voltage accurately, you must connect a load- even a small one.
The load current sets-up the magnetic field the autotransformer needs to work.

73 Dave AB5S